A codebook-based linear precoding scheme in a closed loop multi-antenna communication system is a method of multiplying a transmission signal vector by a matrix selected from a codebook which is a set of a plurality of predefined precoding matrices to transmit it to a plurality of antennas. A receiver selects the precoding matrix in the codebook through channel state information, and an index of the precoding matrix selected by the receiver is fed back to a transmitter. Herein, since the transmitter does not need to have access to the channel state information, the transmitter can be implemented by a low feedback overhead.
A HARQ technique requests retransmission by feeding back a negative acknowledgment (NAK) message to the transmitter at occurrence of an error after judging whether or not a received packet is received without the error by using a cyclic redundancy check (hereinafter referred to as “CRC”) code. The HARQ technique is a scheme that enhances an error probability by combining reception information of a previously received packet and reception information on a newly retransmitted packet.
When the same scheme of selecting a precoding matrix as the initial transmission is used at the time of selecting the precoding matrix in retransmission due to an initial transmission error in the case in which the HARQ technique is adopted in the codebook-based linear precoding scheme, a diversity combining gain cannot be sufficiently obtained through the retransmission. It is possible to select an optimum precoding matrix by utilizing reception information of the initial transmission at the time of using the precoding matrix to be used for the retransmission in the codebook.
In the case of using the related art so as to select the precoding matrix for maximizing the diversity combining gain in the retransmission, the transmitter must have access to the channel state information and must be adopted only in a combining scheme that is capable of concatenating reception signal vectors.
Further, only when channel states in the initial transmission and the retransmission are the same, a study of characteristics of the precoding matrix used for the initial transmission and the retransmission is performed. When corresponding vectors of the precoding matrices used for the initial transmission and the retransmission must have orthogonality, the diversity gain is maximized.
However, the characteristic is generally not satisfied by the codebook and is available only in the case in which a precondition that the channel state must be the same in the initial transmission and the retransmission is satisfied.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.